1. Field of the Invention
The present invention relates to image coding and decoding apparatuses, image coding and decoding methods, an image transmission method and a recording medium. More particularly, the present invention relates to image coding and decoding apparatuses, image coding and decoding methods, an image transmission method and a recording medium suitable for the process of converting, for example, motion picture images on a film into a television signal, encoding, transmitting and decoding the television signal.
2. Description of the Related Art
A motion picture is considered to be, for example, a sequence of photographs developed on a film. To televise such a motion picture or record it on a recording medium such as a video tape, it is necessary to convert images on the film into a television signal. Ordinarily, such conversion is called "telecine" and is made by using a telecine apparatus.
In a telecine apparatus used for such a purpose, an image on a film is read as an electrical signal and is converted into a video signal. The video signal undergoes, for example, display rate conversion and other necessary processings. In this manner, a television signal in accordance with a television broadcasting standard is obtained.
The aspect ratio of images in the form of video frames in the current television broadcasting (the ratio of the lengths of horizontal and vertical sides of display screen) is ordinarily 4:3 while the ratio of the lengths of the horizontal and vertical sides of frames on an ordinary film is approximately 16:9. A telecine process under such a condition requires processing 16:9 frames on a film to form 4:3 frames (frames having an aspect ratio of 4:3).
As a method for such aspect ratio conversion, the edge cropping method, the letter box method and the squeeze method described below with reference to FIG. 8 are known.
According to the edge cropping method (FIG. 8(B)), a portion of a 16:9 frame on a film (FIG. 8(A)) is cut out to form a 4:3 frame. According to the letter box method (FIG. 8(C)), blank spaces (black areas in FIG. 8(C)) are added adjacent to the upper and lower sides of the 16:9 film frame to form a 4:3 frame. According to the squeeze method (FIG. 8(D)), the width of the 16:9 film frame in the horizontal direction is reduced to form a 4:3 frame.
Basically, squeezing of the squeeze method is conversion performed for the purpose of displaying a 16:9 frame on a 16:9 monitor by transmitting the frame as the current television signal (the television signal of the aspect ratio of 4:3).
A sequence of images formed by the edge cropping method (edge-cropped images) and televised or recorded on a recording medium to be sold is produced as described below. Such a sequence of edge-cropped images is obtained not by simply cutting out central areas of a sequence of frames on a film but by a telecine process supervised by the maker who made the sequence of images on the film (e.g., a film director). In the telecine process, image areas to be cut out are designated such as to make a version of the original work, and the designated areas are cut out.
That is, as shown in FIG. 9, information on cutting-out positions on a film designated by a filmmaker is input to a telecine apparatus. The telecine apparatus cuts out portions of frames on the film in accordance with the cutting-out position information, thereby making a sequence of 4:3 edge-cropped images.
For example, a sequence of edge-cropped images made in this manner is encoded and recorded on a recording medium or transmitted over a predetermined transmission channel. On the user side, each edge-cropped image recorded on the recording medium or transmitted over the transmitted channel is reproduced or received. The reproduced or received image is decoded to be displayed on a 4:3 monitor (a monitor having an aspect ratio of 4:3).
A sequence of images formed by the squeeze method (squeezed images) and televised or recorded on a recording medium to be sold is produced as described below. As shown in FIG. 10, each of a sequence of images on a film is filtered in the horizontal direction so that the aspect ratio is set to 4:3, thereby forming a sequence of images elongated in the vertical direction as shown in FIG. 8(D). Each elongated 4:3 image, i.e., a squeezed image, is encoded and recorded on a recording medium or transmitted over a predetermined transmission channel, as is the above-described edge-cropped image.
On the user side, the squeezed image recorded on the recording medium or transmitted over the transmitted channel is reproduced or received and is decoded. If a monitor having an aspect ratio of 16:9 is provided on the user side, the decoded squeezed image is supplied to and displayed on the 16:9 monitor. As shown in FIG. 11, the 16:9 monitor has pixels elongated in the horizontal direction in comparison with pixels of a 4:3 monitor. On the 16:9 monitor, therefore, the squeezed image is displayed in the original state, that is, the image elongated in the vertical direction is displayed by being extended in the horizontal direction.
The above-described squeezed image can also be displayed on a 4:3 monitor, as shown in FIG. 10. That is, a portion of the squeezed image is cut out and up-sampled to form an image having an aspect ratio of 4:3 to be displayed on the 4:3 monitor. The 4:3 image displayed on the 4:3 monitor is equivalent to the image obtained by edge-cropping the image on the film.
However, if a sequence of squeezed images is displayed on a 4:3 monitor in the above-described manner, a problem in terms of copyright arises.
In the case where a sequence of squeezed images converted from a sequence of images on a film by a telecine apparatus is displayed on a 16:9 monitor as shown in FIG. 12, the images on the film are reproduced in the original form on the 16:9 monitor and, therefore, no copyright problem arises. On the other hand, in the case where a sequence of squeezed images converted from a sequence of images on a film by a telecine apparatus is displayed on a 4:3 monitor, there is a possibility of an edge-cropped image without director's approval being displayed, that is, an image cut out from the image on the film irrespective of cutting-out information provided under the supervision of the maker may be displayed.